Python Using List/Multiple Arguments in Pool Map

Question

I am trying to pass a list as a parameter to the pool.map(co_refresh, input_list). However, pool.map didn\'t trigger the function co_refresh

Answer 1

You should define your work function before declaring the Pool, when you declaring Pool, sub worker processes forked from that point, worker process don't execute code beyond that line, therefore not seeing your work function.

Besides, you'd better replace pool.map with pool.starmap to fit your input.

A simplified example:

from multiprocessing import Pool

def co_refresh(a, b, c, d):
    print(a, b, c, d)

input_list = [f'a{i} b{i} c{i} d{i}'.split() for i in range(4)]
# [['a0', 'b0', 'c0', 'd0'], ['a1', 'b1', 'c1', 'd1'], ['a2', 'b2', 'c2', 'd2'], ['a3', 'b3', 'c3', 'd3']]

pool = Pool(processes=3)
pool.starmap(co_refresh, input_list)
pool.close()